The present invention relates to a process for the production of flexible polyurethane foams and the foams produced by that process.
Flexible polyurethane foams may be produced from known flexible foam polyethers. Generally, bi- to trifunctional polyethers in which the polyether chains are made up of ethylene oxide and propylene oxide or of propylene oxide alone and which have propylene oxide and, hence, secondary OH groups are reacted in known manner with TDI-80 (tolylene diisocyanate containing 80% 2,4- and 20% 2,6-isomer).
The hardness of these foams is largely determined by their gross density (foam density). Hardness can only be increased for the same foam density by increasing the TDI index (stoichiometric amount, of TDI to that of the other reaction components with a stoichiometric reaction being 100). Narrow limits are however imposed by such a process.
Since increased foam hardness is a desirable property, attempts to achieve that property by selection of appropriate reactants have been made. Foams of increased hardness are generally produced by one of two methods. In the first of these known methods, active polyethers, i.e. polyethers which contain ethylene oxide residues at the end of the chain and which therefore contain a high proportion of primary OH groups, are used. In the foaming of these active polyethers, TDI-65 (tolylene diisocyanate containing 65% 2,4- and 25% 2,6-isomer) must be used in addition to TDI-80 to avoid the formation of closed cells and shrinkage. However, the stability during foaming (i.e. susceptibility to the disturbances typically affecting foam production) of these systems is basically inferior to systems based on standard ethers and TDI-80.
In the second method, mixtures of standard ethers with filled polyols (polyethers containing an organic filler in finely dispersed phase) are used. In this process, foaming with TDI-80 is possible. This process is also comparable in terms of foaming stability to the processes in which standard polyols are used. However, this second alternative has economic disadvantages with respect to the mixing component used in comparison with the foaming of standard ethers and, generally, in comparison with the processing of active systems using TDI-65.
Not one of the processes aimed at obviating the described disadvantages by using short-chain, polyfunctional crosslinking agents in admixture with standard polyethers to increase compression hardness (including those which afford economic advantages) has acquired any significance for one or more of the following reasons:
(1) The addition of monomeric OH-functional compounds such as glycerol, trimethylolpropane and triethanolamine, even in small quantities (less than 2 percent by weight), leads to shrinkage. Consequently no property improvements can be obtained. PA0 (2) The addition of alkoxylated polyamines or polyfunctional alcohols, possible in quantities of up to 5 percent by weight, significantly impairs the open-cell character, tensile strength and breaking elongation without appreciably increasing compression hardness. PA0 (3) The addition of alkoxylated polyhydric alcohols PA0 (4) The addition of crystalline, polyhydric alcohols such as sorbitol, finely dispersed in the polyether (disclosed in DE-OS No. 2,507,161) requires melting of the polyfuactional alcohol component during the foaming process to achieve the described effect of increasing compression hardness. PA0 n=2-4, preferably 2, and PA0 Q represents an aliphatic hydrocarbon radical containing from 2 to 18 (preferably from 6 to 10) C-atoms, a cycloaliphatic hydrocarbon radical containing from 4 to 15 (preferably from 5 to 10) C-atoms, an aromatic hydrocarbon radical containing from 6 to 15 (preferably from 6 to 13) C-atoms or an araliphatic hydrocarbon radical containing from 8 to 15 (preferably from 8 to 13) C-atoms.
having OH numbers of up to 120 does lead to open-cell foams, but the increase in hardness is minimal and the tensile strength and, above all, breaking elongation of the resulting foams are adversely affected due to the large quantities which have to be added.
As described in GB-PS No. 1,396,105, propoxylation products of polyhydric alcohols, such as trimethylolpropane and pentaerythritol, having OH numbers around 175 may be co-foamed in 9 parts without any problems. However, no increase in compression hardness is obtained.
According to GB-PS No. 1,396,105 and DE-OS No. 3,323,872, foams combining increased compression hardness with other favorable mechanical properties are obtained by using adducts of alkylene oxides (ethylene oxide and/or propylene oxide) and monomeric, polyfunctional alcohols having a functionality of .gtoreq.6 and OH numbers of from 120 to 200 which are compatible with standard polyethers in admixture with standard polyethers. The disclosed alkylene oxide adduct may be used in quantities of up to 20 wt. % using standard flexible-foam formulations, preferably formulations based on TDI-80.